These studies are investigating lead (Pb) toxicity at doses generally below or sometimes just at the threshold producing such clinical symptoms as marginal hematocrit depression or mild appetite loss. Pb is being administered at various developmental stages (in utero, first half year of life, second half year of life, combinations of the preceding, or to adult animals). Measures of Pb dosage include amount of Pb intake on a daily basis, blood lead (PhB) levels of the mothers and of the offspring after parturition, and lead levels in mother's milk (PbM) where appropriate. Attempts will be made to identify a Pb-binding ligand in mother's milk. Measures of toxicity include clinical assessments of general health, appetite and hematocrit, and measures of behavioral toxicity (on which the studies are focused). Selected animals will be sacrificed to study Pb distribution in body tissues, with regional analysis of brain content, and to study neuroanatomic lesions. The particular interest of the present experiments is in analysis of long-term behavioral deficits. We have already observed deficits in scotopic visual function, reversal learning and a spatial memory task in animals several years after Pb exposure given throughout the first year of postnatal life. These tasks will be investigated in monkeys at similar ages from other conditions of early Pb exposure. In addition, other tasks will be studied, especially a battery of tasks associated with hippocampal dysfunction in the monkey. These data, both behavioral and neuroanatomic, will be examined to determine if a large component of Pb neurotoxicity can be explained as amygdalo-hippocampal damage. Visual masking also will be investigated to measure if Pb toxicity has slowed stimulus identification processing.